PLATE VIII— Continneil. 



LepTyENA rhomboidalis, Wilckens. 



Fig. 17. The exterior of a larg-e pedicle-valve, which is unusually extended on the hinge-line and with acute 



cardinal extremities. 



Niagara group. Lockport, JV. T. 

 Fig. 18. An enlargement of the articulating apparatus of the bi-achial valve ; showing the central groove 



of the deltidial callosity, the lobes of the cardinal process, and the dental sockets with their 



low, thick inner walls (crural plates). X 3. 

 Fig. 19. The interior of a brachial valve. 



Niagara group. JValdron, Indiana. 

 Fig. 20. A view of the brachial valve ; showing a foi-amen in the beak. 



Fig. 21. A iirofile view of a strongly geniculated specimen ; showing the contour of the two valves. 

 Fig. 22. An enlargement of the beaks of an old individual ; showing the great obliquity of the foramen in 



the pedicle-valve, which penetrates the substance of the shell at a considerable distance in 

 . advance of the apex ; and also the pei'foration in the deltidinm of the opposite valve.> 

 Fig. 23. A cardinal view of a specimen where the deltidium of the pedicle-valve has been lost oi' absorbed 



and the sjiace filled by the callosity of the opposite valve which is perforated at the apex. 

 Fig. 24. The interior of a brachial valve ; showing the aspect of the canlinal process from this point of 



view, the charactei' of the muscular scars, and the strong I'idge at the line of genicnlation of 



the valve. 

 Fig. 25. The interior of a pedicle-valve ; showing the character of the muscular impressions. 

 Pig. 26. An enlai-gement of the central cardinal portion of a brachial valve ; showing the deltidial callus, 



and the slit formed by the receding or wearing of the apical perforation. 

 Fig. 27. An enlai'gement of the inteiior of the pi'eceding speitimen ; showing the same features, and also 



the tubular ojiening- into the rostral cavity between the divisions of the cardinal process. 

 Lower Helderberg group. Albany and Schoharie counties, N. T. 

 Fig. 28. The extei'ior of an exfoliated pedicle-valve ; showing very strong undulations and the groove left 



by the I'eceding of the apical foramen. 



Fig. 29. The exterior of a pedicle-valve, in which the undulation? are liner and much more numerous than 

 usual. (The L. undulata of Vancxem.) 



Coi-niferous limestone Western New York. 

 Fig. 30. The exterior of a pedicle-valve. 

 Fig. 31. The interioi' of a brachial valve. 



Waverly group. Mallets' Creek, Ohio. 



